It is known from EP0752541 (ArvinMeritor, Inc.) to provide formations on a pair of brake pads and corresponding features in abutment surfaces of a brake carrier to inhibit the brake being fully assembled with the pads orientated with the backplate thereof facing the brake disc. Incorrectly fitting brake pads in this manner is highly undesirable since the braking effectiveness of the brake is dramatically diminished and damage to the pad and brake disc may also occur.
In this patent, the two pads are identical and are provided with a formation that has rotational symmetry about an axis extending perpendicular to the rotational axis of the brake disc, so that although the pads cannot be fitted with the backplate facing the disc, the pads are interchangeable in an inboard and outboard sense.
In most applications such an arrangement is entirely satisfactory. However, the inventors have recognised that in some circumstances further measures may be required to ensure that in an “abuse” situation a user cannot forcibly refit the pad retainer. This situation may arise because the vertical height difference between the stepped pad abutments required to lift an incorrectly orientated pad is limited by the strength requirements of the brake carrier. A suitable step height in the pad assembly and corresponding carrier abutment 62, 63 for an optimised carrier and to prevent the incorrect installation can have a marked reduction in usable pad volume.
EP1473481 (BPW) discloses alternative pad foolproofing arrangements. In one embodiment, lugs having rotational, but not mirror symmetry are provided in a non-machined portion of the pad windows, proximate the machined surfaces. This location is undesirable as it is a high stress area of the carrier, and may result in uneven wear of the pad, as one of the two pistons exerts the same braking force, but over a lower pad area.
In another embodiment, the lugs have mirror symmetry and are configured only to extend into a corresponding cut-out in the metal backplate, but not the friction material. In both embodiments, a part-worn pad can be fitted in the incorrect window facing the wrong way.
In service, part worn pads may be removed and refitted, e.g. to inspect the pads for signs of cracking and glazing, so the applicant recognises that a real risk that impaired brake function may occur if such pads are wrongly fitted.
The present invention seeks to overcome or at least mitigate the problems of the prior art.